Exemplary embodiments relate to a method of operating a nonvolatile memory device and, more particularly, to a method of operating a nonvolatile memory device, which is capable of reducing a bit line precharge time when data are read.
A nonvolatile memory device may have the advantages of random access memory (RAM), such as enabling the writing and erasure of data, and read only memory (ROM), such as retaining data even without the supply of power, and so has recently been widely used for the storage media of portable electronic devices, such as digital cameras, personal digital assistants (PDAs), and MP3 players.
The nonvolatile memory device may include a memory cell array, a row decoder, a page buffer unit, etc. The memory cell array includes a plurality of word lines elongated in rows, a plurality of bit lines elongated in columns, and a plurality of cell strings corresponding to the respective bit lines.
Memory cells may have varying threshold voltages according to their program states. It is ideal that the memory cells have the same threshold voltage according to the state of data to be stored. However, when a program operation is actually performed on the memory cells, the threshold voltages of the memory cells have probability distributions in some regions because of various external environments, such as the device characteristics and the coupling effect.
When reading programmed data, the nonvolatile memory device may consecutively perform operations, such as bit line precharge, bit line evaluation, sense, and discharge.
The bit line precharge operation is performed to precharge a bit line, coupled to a selected memory cell, to a desired voltage level so as to read data. The bit line evaluation operation is performed to change a precharged bit line according to the program state of a selected memory cell.
The sense operation is performed to sense the voltage of a bit line changed through an evaluation operation and to latch the sensed voltage. The discharge operation is performed to discharge the voltage of a bit line.
The bit line precharge operation may have the longest execution time in the data read process. This is because a bit line is precharged to a desired voltage level using the sense node of a page buffer.